Integrated circuit design and fabrication is a vastly difficult effort and involves complex interaction among numerous aspects of the circuit being designed. Analog circuit design further complicates the design process because of interactions among the numerous devices of the design. Detailed understanding of active and passive device operation, timing, and interaction within a circuit is critical to successful circuit design. Scaling of the devices must result in correct circuit operation during all phases of operation. Large numbers of devices may be present in an integrated circuit; frequently millions and even hundreds of millions of transistors are included. Each transistor, composed of shapes for diffusion, polysilicon, contacts, metallization, and other structures, must be correctly scaled in order to operate properly. The ability to design chips with such large numbers of essential transistors can be quite challenging and needed optimization of the circuitry can be a daunting task even with the help of electronic design automation (EDA) software tools.
There are numerous devices of miniscule dimension in close proximity to one another on each semiconductor chip. Detailed analysis of the analog aspects of the devices is critical to successful circuit design. Signal voltages, noise, device scaling, and the like must all be considered. All of the transistors must be properly scaled and fabricated to exacting specifications. As technologies have advanced, smaller and smaller lithographic dimensions are used. These smaller dimensions require smaller signal voltages and closer design tolerances of the devices. Signal noise, leakage current, and the like are also critical design considerations. Each of these and other design parameters must be carefully considered in order for the circuit of interest to function properly. Significant design effort is required during the development process. Circuit designers require complex tools in order to analyze and scale the devices especially as circuits interact with each other. Various conditions under which a circuit needs to operate must likewise be evaluated.